name: testing-strategy agents: [yokay-test-runner] description: Use when designing test architecture, building API test suites, validating API contracts, setting up component or E2E testing, managing test data, debugging flaky tests, reviewing coverage strategy, or organizing test files. Covers test pyramid, mocking (MSW), frontend (React Testing Library, Playwright), and CI integration.

Testing Strategy

Comprehensive testing guidance for test architecture, coverage strategy, and test design.

Test Pyramid

Key Principles

• Test behavior, not implementation — test what code does, not how
• Follow the testing pyramid — more unit tests, fewer E2E
• Use meaningful coverage metrics — branch coverage over line coverage
• Prevent flaky tests — no arbitrary waits, no test interdependence

Quick Start Checklist

1. Choose test framework (Vitest recommended for new projects)
2. Design test folder structure mirroring source
3. Write unit tests for pure logic and utilities
4. Add integration tests for API endpoints and data flows
5. Add contract tests against OpenAPI spec (if applicable)
6. Add E2E tests for critical user journeys only
7. Set up CI to run tests on every PR

What NOT to Test

• Framework internals (React rendering, Express routing)
• Third-party library behavior
• Trivial getters/setters with no logic
• Implementation details (private methods, internal state)

References